The need to define the events of tumor-host interactions in modern immunological terms is apparent. By using autochthonous or transplanted syngeneic tumors in mice (including spontaneous mammary tumors, chemically induced fibrosarcomas and lung adenocarcinomas) we will attempt to define: the dynamics of development of immunity after immunization; the dynamics of development of concomitant immunity in the tumor bearing host; the cell types involved in the response and regulation of such respone; the antibodies produced during such responses and the significance of the different tumor-associated antigens in triggering "selectively" humoral or cellular immunity. The mammary tumor in mice has some intrinsic advantages for the study of such events since some of the viral antigens are relatively well defined biochemical entities. One of the major problems for the study of the role of antigen or antigen-antibody complexes in other tumor systems has been the undefined nature of such antigens. Both by selective stimultion or inhibition in vivo and in vitro of the immune lymphoid cells we will be able to define the significance of such antigens as stimuli for the host immune response. The correlation of the in vitro technology with in vivo assays will emphasize the biological significance of such events. The information generated by such approach could be used for a rational investigation of specific and non-specific immune potentiation.